AbstractionA mentalmodel that removescomplex details1.1Computing Systems7each step in turn and you will be amazed at how well it all falls intoplace.AbstractionThe levels of a computing system that we just examined are examples ofabstraction. An abstractionis a mental model, a way to think about some-thing, which removes or hides complex details. An abstraction leaves onlythe information necessary to accomplish our goal. When we are dealingwith a computer on one layer, we don’t need to be thinking about thedetails of the other layers. For example, when we are writing a program,we don’t have to concern ourselves with how the hardware carries out theinstructions. Likewise, when we are running an application program, wedon’t have to be concerned with how that program was written.Numerous experiments have shown that a human being can activelymanage about seven (plus or minus two, depending on the person) piecesof information in short-term memory at one time. This is called Miller’s
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